A fiber-reinforced composite material is widely used as a light structural material. A reinforcement base for a fiber-reinforced composite material includes a fibrous structure formed from textile. A composite material formed by the fibrous structure and a matrix resin is used as a structural material for rockets, airplanes, bicycles, ships, and buildings.
Patent document 1 discloses an example of a fibrous structure. As shown in FIG. 6A, a fibrous structure 80 of patent document 1 includes a flat base plate 81 (main plate) and a T-shaped rib 82 (sub-plate) that is coupled to the base plate 81 by thickness-wise direction yarns 83.
The T-shaped rib 82 includes two L-shaped fibrous structures 82a that are coupled to each other. The thickness-wise direction yarns 83 are extended along a portion of the rib 82 overlapping the base plate 81 to couple the rib 82 and the base plate 81. However, the portion of the rib 82 where the thickness-wise direction yarns 83 extend increases the weight and material cost of the fibrous structure 80.
Patent document 2 discloses a method for manufacturing a main plate and a sub-plate, which intersects the main plate, from fiber layers that have been woven in advance. As shown in FIG. 6B, in the manufacturing method disclosed in patent document 2, a fiber layer 90 that forms a horizontal main plate and a fiber layer 91 that forms a sub-plate, which is perpendicular to the main plate, are first woven integrally with each other. The two fiber layers 90 and 91 are formed by weaving warps and wefts. The textile is opened from an intersecting portion of the two fiber layers 90 and 91 to form the main plate and the sub-plate and manufacture a fibrous structure having the desired shape.